1. Field of the Invention
The invention relates to methods for forming insulated coils for electrodynamic machines, and in particular stator coils suitable for alternating current (AC) induction motors. Coils formed by the present invention provide for machine winding of insulating tape about the coil circumference prior to bending and spreading the coil to its final, three-dimensional rigid configuration without the need for application and removal of temporary sacrificial protective tape as part of the spreading process. Application of the present invention method reduces the need for hand taping the coils after bending and shaping operations.
2. Description of the Prior Art
Electrodynamic machines generate electromagnetic forces (EMF) between a rotor and stator that are in relative motion. The general physical principles, construction and operation of AC motors is known to those skilled in the art. The exemplary known alternating current induction motor 20, shown in FIGS. 1 and 2, has a rotating rotor 25 and shaft 26. Torque generated on the rotating shaft 26 enables the motor 20 to perform useful work. A rotating magnetic field induced within poles formed within a stator ring 30 generates EMF that rotates the rotor 25 and shaft 26.
The AC induction motor 20 stator ring 30 has a stack of annularly shaped stator lamina 32 that form radial slots 33 extending generally axially from one end of the rotor to the other. The stator lamina radial slots 33 receive stator coils 35 that are arrayed in poles about the circumference of the stator ring 30. Application of current sequentially to the stator poles induces rotating magnetic fields in the stator ring 30. The induced EMF in turn causes rotation of the rotor 25 and shaft 26.
An exemplary known stator coil 35 is shown in FIGS. 3 and 3A. The stator coil 35 is a wound continuous conductive wire bundle that is formed into a three dimensional shape. The coil 35 has a pair of generally parallel straight sections 36A and 36B having respective generally rectangular cross sections that are oriented for insertion into the radial slots 33 formed by the stator ring lamina 32. In order to accomplish the desired radial orientation of the straight sections 36A and 36B within the radial slots 33, the coil 35 is formed with end portions 37A and 37B, often having a compound curve U-bends 38A and 38B. Leads 39 provided on the coil end portion 37A are coupled to an electric current power source. When current is applied to the leads 39, an electromagnetic field is induced within the coil. As is known by those skilled in the art, the continuous ribbon wire 40 forming the coil 35 has an insulating outer layer coating in order to optimize the magnetic field strength induced within the coil. The wire 40 is typically constructed of copper and coated with a resin or other electrically insulative layer that is thin relative to the wire dimensions.
As is well known in the art, individual stator coils 35 are electrically isolated from their surrounding environment by a circumferential insulation layer, often a multi-layered combination of tape and hardened resin. The insulating layer is applied using known techniques. In FIGS. 3 and 3A, the insulation layer 42 is depicted schematically as a spiral wrapped circumferential layer of tape 44 that is thereafter coated with a multi-part epoxy resin 46. Often stator coils are supplied to motor manufacturers with only the spiral wrapped tape layer 44, ready for application of the resin 46 by the motor manufacturer. Application of a resin coating over a wrapped coil is not part of the present invention and is not specifically claimed herein.
In the past, the stator coil insulation layer 42 was often applied after final forming of the coil wire bundle to its final intended shape. The earliest forms of tape insulation application were performed totally by hand. Later, cost savings were achieved by utilizing machine wound tape layers on the straight sections 36A and 36B. However, the compound curved end portions 37A and 37B and the coil leads 39 still needed to be tape-wrapped by hand labor. Hand taping is expensive, time consuming, and may be prone human error. Generally it has not been found practical to machine wind the compound curved end portions 37A and 37B, including the U-bends 38A and 38B, or the leads 39 after the coil is formed to its final intended configuration.
Generally it has been the opinion of those in the art that insulation should be applied to stator coils after completion of their forming operations, to prevent risk of insulation damage during the forming operations. In some instances, manufacturers have applied insulating tape to straight portions of the stator core wire bundles followed by application of a temporary sacrificial layer of protective tape, prior to their shaping/bending forming operations. The temporary sacrificial tape layer was thought to reduce likelihood of mechanical damage or abrasion on the insulated wire strand 40 and/or heat migration of melted resin from the tape during the high-pressure, elevated temperature forming steps. The temporary protective sacrificial tape layer then needed to be stripped from the formed coil after the formation steps. Thereafter the now fully formed stator coil was fully insulated by completion of insulating tape 44 wrapping operations and resin impregnation 46, using known techniques.
Thus, a need exists in the art for a method for forming electrodynamic machine coils that reduces taping operations, including temporary application of sacrificial tape during coil manufacture, and preferably replaces hand taping with machine taping operations. While it may not be feasible in all manufacturing operations to replace all hand taping with machine taping processes (for example, localized taping around stator coil leads), reduction of taping operations reduces costs and likelihood of taping errors in the eliminated extra steps.